1. Field of the Invention
The present invention relates to a movable contact unit with a light-guiding function for structuring the operation panel of electronic equipment and also relates to a lighted panel switch using the movable contact unit.
2. Background Art
Conventionally, key switches with a lighting function have frequently been used for an operation panel mounted on electronic equipment, such as a mobile phone or a handheld terminal. In such a lighting function, light of an LED directly illuminates keys on the panel or the light of an LED is guided to the keys through a light-guide sheet or the like.
FIG. 2 is a section view of part of a conventional input device. Circuit board 100 of FIG. 2 has central fixed contact 101 and peripheral fixed contact 102. Sheet material 110 is disposed on the upper surface of circuit board 100 via adhesive layer 111. Sheet material 110 and adhesive layer 111 form dome section 120 that protrudes upward in which dome-shaped movable contact 130 is accommodated. The circumferential end of dome-shaped movable contact 130 is mounted on peripheral fixed contact 102 in a manner such that the center of the dome faces central fixed contact 101 at an established interval. The upper surface of domed movable contact 130 is held by adhesive layer 111 disposed beneath sheet material 110. Sheet material 110 is a light-guide sheet of an insulation film, for example, made of polycarbonate. The light-guide sheet guides light incident from the side end and illuminates the upper side of the sheet.
Light-emitting device 150 is mounted on circuit board 100. The light of light-emitting device 150 comes in parallel with sheet material 110 that guides light. Taking the route of light into account, light-emitting section 151 is disposed opposite to the side end of sheet material 110. Transparent resin-member 160 gathers light from light-emitting section 151 and effectively guides the light incident from the side end of sheet material 110.
Next will be described the workings of such conventional input device. When dome section 120 is pushed with a predetermined magnitude of force, movable contact 130 disposed in dome section 120 bends down and makes contact with central fixed contact 101. This brings electrical connections between central fixed contact 101 and peripheral fixed contact 102 via movable contact 130, establishing the ON state of the switch. When the pushing force is removed, movable contact 130 returns to its original shape, i.e., the switch goes back to the OFF state (FIG. 2).
When light is emitted from light-emitting device 150 that is disposed at the side end of sheet material 110 as a light-guide sheet, the light is guided inside the light-guide sheet including the dome-shaped space formed by dome section 120, so that the upper side of sheet material 110 is illuminated. The structure above has greatly increased ease of operation; when input keys having letters and symbols marked thereon made of light-transmissive material are disposed on sheet material 110, they are easily recognized, particularly in the dark. For example, Japanese Unexamined Patent Application Publication No. 2007-53063 is known as a patent document relating to the structure above.
According to the conventional input device, as described above, a light-guide sheet, i.e., sheet material 110 is disposed along the domed shape of movable contact 130. At the same time, adhesive layer 111, which is used as the adhesive layer for circuit board 100, is disposed on the lower surface of sheet material 110. If difference in refractive index of light between adhesive layer 111 and sheet material 110 is small, the light traveling through sheet material 110 passes at the interface between adhesive layer 111 and sheet material 110, thereby increasing the loss in amount of light at the interface between the adhesive layer and circuit board 100. Moreover, the light travelling through adhesive layer 111 is absorbed or scatters inside adhesive layer 111, thereby increasing the loss in amount of light. In some cases, the reflected or scattered light inconveniently leaks on the upper side of sheet material 110, resulting in poor illuminance in the operation panel that is to be lighted. Even in the structure where adhesive layer 111 is partly removed, if sheet material 110 makes contact with circuit board 100 or movable contact 130, the light traveling through sheet material 110 reflects or scatters at the interface between adhesive layer 111 and sheet material 110, thereby increasing the loss in amount of light at the interface.